Democrat Conor Lamb, a former U.S. attorney and U.S. Marine Corps veteran running to represent Pennsylvania's 18th congressional district, speaks to an audience at the American Legion Post 902 on January 13, 2018 in Houston, Pennsylvania.

Republicans are hoping to hold off an election disaster in another red pocket of the country.

On Tuesday, election handicapper Cook Political Report changed its rating for next month's Pennsylvania House special election to "toss-up" from "lean Republican." The race for Pennsylvania's 18th District — which President Donald Trump won by 20 points in 2016 — appears close with only two weeks until voters head to the polls.

A win by Democratic candidate Conor Lamb would give the minority party in Congress hope about its ability to compete in red districts and potentially win back the House in November. A victory for Republican Rick Saccone would curb Democratic optimism and show the GOP that a strong economy and its new tax law may help it hold both chambers of Congress.

Cook's rating change came as Lamb announced a $3.2 million fundraising haul from Jan. 1 to Feb. 21. Lamb's campaign hits its final stretch without any more financial support from House Democrats' fundraising arm and facing a barrage of spending from Republican outside groups.

Such outside organizations have shelled out $4.8 million opposing Lamb and $2.2 million supporting Saccone, according to the Center for Responsive Politics. Conversely, outside groups spent only about $384,000 against Saccone and roughly $244,000 for Lamb.

The Saccone campaign has not yet released its own fundraising figures for the beginning of the year. It has to file a financial report with the Federal Election Commission later this week. A campaign spokesman did not immediately respond to CNBC's request to comment.

Limited polls taken in the race have shown an edge for Saccone, a 60-year-old member of the Pennsylvania House of Representatives. A Gravis poll this month found a 6-percentage-point advantage for the Republican, while a Monmouth poll showed a 3-percentage-point edge. The election is scheduled for March 13.

On Tuesday, Lamb's campaign tweeted that it has seen a competitive race "for weeks."

"The race is a tossup & Conor can win," the campaign said.

The candidates

Republicans aim to tie Lamb, a 33-year-old attorney and Marine veteran, to House Democratic Leader Nancy Pelosi, who is broadly unpopular nationally. In recent attack ads, the pro-GOP Congressional Leadership Fund has called Lamb and Pelosi "too liberal" and hit the Democratic candidate for criticizing the Republican tax plan. Lamb has echoed many in his party in arguing the plan cut tax rates too steeply for the wealthy and corporations, and not enough for the working class.

This week, the Democrat used an ad to distance himself from Pelosi.

"My opponent wants you to believe that the biggest issue in this campaign is Nancy Pelosi. It's all a big lie," Lamb said. "I've already said on the front page of the newspaper that I don't support Nancy Pelosi. The real issues are the ones that affect your lives."

In a speech last month near the western Pennsylvania congressional district, Trump repeatedly promoted the tax cuts as a boon for the middle class and small businesses. In a January tweet, he called Saccone a "great guy" and said "we need more Republicans to continue our already successful agenda!"

One area where Lamb has taken a more moderate stance than many Democrats is gun control. He has not endorsed new gun laws and instead focused on improving the existing background check system and making sure people with mental illnesses do not access guns.

Public support for tighter gun restrictions has mounted since the shooting massacre of 17 people at a Florida high school on Feb. 14. While Democrats generally support tougher gun laws, Lamb has tiptoed around the issue in the typically Republican district.

Republican Rep. Tim Murphy held the seat, situated outside of Pittsburgh, for more than 14 years. The pro-life congressman resigned last year after allegedly urging his lover to get an abortion.